The friction of Gantry fiveaxis machine tools affects the feeding and positioning accuracy,leading the increase of synchronization error and influencing the machining accuracy of the workpieces.With the friction coefficient of sliding rails as variable,the transient dynamic simulation analysis of Gantry fiveaxis machine tools was carried out by workbench.The effect of friction on the machine tools precision under dry friction was analyzed,and the zigzag error was confirmed by the experiment of Renishaw laser measurement.The result proves that the change of rail friction coefficient will cause machining error.With the increasing of friction coefficient,the error in each direction is increased almost exponentially.The error is increased in regular when friction coefficient is in the range of 0 to 02,while the error changes with no rule when the friction coefficient is 03.The result of Laser Interferometer measurement shows the motion error angle varies with the distance increase,indicating the presence of unsynchronized error in the X direction,and swing error in the Y direction.